Elastic metadata and multiple tray allocation

In some examples, both object data and corresponding metadata are stored on thin provisioned block storage in which blocks for the storage of the object data and the metadata are dynamically provisioned from a shared pool. For instance, the metadata may be stored on the block storage using a tree data structure that may grow proportionally with the corresponding stored object data. The object storage may automatically adapt to the size and number of objects being stored, and storage space for metadata may be allocated dynamically on demand. Additionally, some implementations include storing data across multiple trays. For instance, a plurality of storage extents of an extent group may be allocated across a plurality of storage devices on multiple trays. The extent allocation may be tray-aware by allocating extents to maximize the probability that data remains available/recoverable in the presence of a failure in one or more trays.